The present invention relates to a chemical liquid supply technique of discharging a predetermined amount of liquid from a chemical liquid or the like, which is preferably used to coat a processing liquid such as a photoresist liquid or the like onto a surface of a semiconductor wafer.
Chemical liquid such as photoresist liquid, spin on glass liquid, polyimide resin liquid, pure water, developing liquid, etching liquid, washing liquid, organic solvent, and the like are used in manufacturing processes in various technical fields such as techniques of manufacturing a liquid crystal board, a magnetic disk, a multi-layered wiring board, and the like, starting from a semiconductor wafer manufacturing technique.
For example, in case of coating a photoresist liquid onto the surface of the semiconductor wafer, the photoresist liquid is dropped onto the surface of the semiconductor wafer from a nozzle, after having rotated the semiconductor wafer in the horizontal plane. In a chemical liquid supply apparatus used for coating this kind of photoresist liquid, a filter is provided to eliminate air bubbles and foreign substances in the photoresist liquid. If a portion of the photoresist liquid contained in a liquid tank is gelled, this gelled portion becomes a foreign substance. If the gelled foreign substance is coated onto the semiconductor wafer, the manufacturing yield on the semiconductor integrated circuit device is deteriorated.
In a conventional chemical liquid supply apparatus, there is provided a pump of a variable volume type which is constructed by an elastically deformable tube or a bellows, in order to discharge a predetermined amount of liquid from a photoresist liquid or the like. In the conventional chemical liquid supply apparatus having this kind of pump, a filter is provided in the secondary side of the pump, or in the discharging side, so that the liquid is permeated through the filter by discharging pressure of the pump. The filtered liquid is dropped from the nozzle provided in the secondary side of the filter (for example, U.S. Pat. No. 5,527,161 and 5,490,765).
Thus, in case where a filter is provided in the secondary side of a pump, a liquid is filtered by the filter when the liquid is discharged from a nozzle in accordance with the discharging operation of the pump. Therefore, the flow rate or flow velocity of the liquid from the nozzle is equal to the flow rate or flow velocity during filtering within the filter.
The photoresist liquid is gelled sometimes. If the photoresist liquid including a gelled portion is coated on a semiconductor wafer, the manufacturing yield on semiconductor integrated circuit devices is lowered. Likewise, if the photoresist liquid with air bubbles is coated, the yield is lowered. A filter is provided in order to capture the gelled portion and air bubbles. By the type of the photoresist liquid and the discharged amount thereof, that the gelled portion and air bubbles pass through the filter in some cases. That is, if the discharge velocity of the liquid discharged from the pump is set in correspondence with the discharge velocity of the from the nozzle and if a chemical liquid is supplied to the filter at the discharge velocity, air bubbles or a gelled portion of the liquid also permeates through the filter in some cases.
As a result of experiments, since chemical liquids such as a photoresist liquid and the like have different viscosities and the like depending on the types of the chemical liquids. Therefore, it has been found that there are optimum discharge flow rates from the nozzle which are respectively inherent to the types of the chemical liquids, as well as optimum permeation flow rates through the filter which are also respectively inherent to the types of the chemical liquids. It has also been found that if the permeation flow rate of the chemical liquid which is let permeate through the filter is set to be smaller than the discharge flow rate from the nozzle, it is possible to effectively capture portions of impure quality such as portions gelled by the filter and air bubbles.